1. Field of the Invention
This document relates to a display device, and more particularly, to a display device which prevents penetration of external moisture and oxygen and has an improved lifespan.
2. Discussion of the Related Art
In recent years, various flat panel displays capable of reducing weight and volume which are demerits of a cathode ray tube have been developed. The flat panel displays include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), and an organic light emitting display (OLED).
Among the above flat panel displays, the organic light emitting display is a self-emissive display device which electrically excites organic compounds and emits light. The organic light emitting diode does not require a backlight unit, unlike liquid crystal display. Therefore, the organic light emitting display may be fabricated in a lightweight and thin type and by simple processes. In addition, since the organic light emitting display may be fabricated at a low temperature and has characteristics of a fast response speed less than 1 ms, low power consumption, a wide viewing angle, and high contrast.
The organic light emitting display comprises an emission layer between an anode and a cathode. Thus, holes supplied from the anode combine with electrons supplied from the cathode in the organic emission layer to form hole-electron pairs, i.e., excitons. When the excitons transition from an exited state to a ground state, energy is generated so that the organic light emitting diode emits light.
FIG. 1 is a cross-sectional view showing a conventional organic light emitting display, and FIG. 2 is a top plan view showing an organic light emitting display which is shrunken.
Referring to FIG. 1, the conventional organic light emitting display comprises a first electrode 12 formed on a substrate 10, a bank layer 13 formed on the first electrode 12, an organic emission layer 14 formed on the first electrode 12 exposed by the bank layer 13, and a second electrode 12 formed on the organic emission layer 14. A passivation film 17, which covers the elements disposed below it including the second electrode 15, is formed, and an encapsulation substrate 24 encapsulates the substrate 10 through an encapsulating agent 22.
Although the above-described conventional organic light emitting display 10 has the passivation film 17 formed on top of the second electrode 15 to protect the elements disposed below it, an impurity 20 with a large diameter may be attached in the fabrication process of the passivation film 17. In this case, external moisture or oxygen penetrates the organic emission layer 14 through a gap in the passivation film 17 that comes off by the impurity 20. As shown in FIG. 2, the organic emission layer 14 has the problem of shrinkage which degrades the organic emission layer 14 by the penetrating moisture and oxygen and causes it to emit no light.